CHULA VISTA  Often teased by schoolmates for masking the marks of his chemotherapy with a beanie, Christopher Rivera, a 13-year-old mixed martial arts fighter, never fought back.

Having battled inside a cage before, Christopher, a seventh-grader at Bonita Vista Middle School, was saving all of his strength for the biggest fight of his life — a bout against Hodgkin’s lymphoma.

Christopher’s mother, Angelina Carrillo, was initially apprehensive about allowing her son to participate in such an inherently violent sport when he began MMA at age 11.

She wasn’t aware that Christopher — like all other kids participating in youth MMA under the United States Fight League — must wear shin guards and padded gloves. Novice fighters are limited to grappling only. Under no circumstances is a fighter under 18 allowed to compete with full contact, according to USFL President John Frank.

Two years after Christopher joined Alliance Training Center in Chula Vista, Carrillo is now fully aware of the rules and thanks the sport for forcing her son to notice an uncomfortable bump on the left side of his neck.

The bump, as it turns out, was the product of stage 2B Hodgkin’s lymphoma. Christopher’s family was devastated by the news.

“I just started to bawl,” Carrillo said. “When you think of the word ‘cancer’ you think of death and I pictured my son dying.”

Christopher’s family wasn’t sure how they were going to break the news to him — nobody had the heart to tell him.

“As a father, I felt it was my responsibility to let him know,” Christopher’s father, Carlos Rivera, said. “I didn’t quite tell him, ‘You have cancer,’ as much as I broke it down for him.”

Surprisingly enough, the young fighter wasn’t devastated by the news.

“It was a big deal,” Christopher said. “But, to me, I was never real nervous or scared.”

Christopher spent three months in and out of the hospital undergoing intravenous and oral chemotherapy.

Professional MMA fighters Brandon Vera and Phil Davis visited Christopher in the hospital with a T-shirt signed by professional fighters from all around the country.

Few people were more devastated by Christopher’s diagnosis than Danny Martinez, UFC fighter and kids MMA coach at Alliance.

Even fewer people were more excited to see Christopher come back to Alliance Training Center.

“It was awesome,” Martinez said of seeing Christopher return to the gym after three months away. “I told him that when he came back he would need to take it slow and take it easy.”

Christopher claims he’s not fully recovered from the therapy — but his accomplishments inside the cage seem to dictate otherwise. Since returning, Christopher has laid claim to three tournament titles — the most recent one coming several weeks ago at Barona Resort & Casino.

Though Carrillo is proud of what her son has accomplished inside the cage, she’s more excited for what he’s capable of on the outside.

Said Carrillo: “I hope that Christopher can see that by being him and doing what he’s doing now, he can show other kids that they can be healed and continue to do the things they were doing.”